The present invention relates to a method for the preparation of an organopolysiloxane composition or, more particularly, to a method for the preparation of an organopolysiloxane composition suitable for the preparation of a shaped silicone rubber article with good mold-releasability.
Silicone rubber compositions for mold preparation having good mold releasability have been widely used heretofore for duplication or replica preparation of cultural assets or artistic handcrafts. Along with the development of electric and electronic industries as well as automobile industries in recent years, these silicone rubber compositions have found applications in the production of industrial products such as parts of electric and electronic appliances as well as parts of automobiles in these industries.
Therefore, such silicone rubber compositions for mold preparation use are required to be suitable for producing duplicates having a complicated configuration exquisitely in large numbers. In addition, it is essential that the mold fabricated from the composition may have a high strength to be durable with good usability. Furthermore, the silicone rubber-made mold prepared from the silicone rubber composition should withstand the adverse influences of certain resinous materials in contact therewith, which may cause deterioration of the silicone rubber.
In order to satisfy these requirements, several methods have been proposed to obtain an improved silicone rubber composition including, for example, a method of compounding a hydrophobic silica filler after a treatment to be provided with surface-blocking organosiloxy groups represented by the formula R.sub.3 SiO.sub.0.5, in which R is a monovalent hydrocarbon group, with an organopolysiloxane having molecular chain terminals blocked each with a silanol group (cf. Japanese Patent Publication No. 47-30422) and a method of compounding a reinforcing filler with an organopolysiloxane having a vinyl group at each of the molecular chain terminals thereof using a nitrogen containing organosilicon compound (cf. Japanese Patent Publication No. 40-19178). However, silicone rubber compositions obtained by these methods are still accompanied by a disadvantage that the above-mentioned requirement for the improvement in the durability of the mold-releasability is hardly obtained.